Genes, lost and found

There's a famous anecdote about British biologist J. B. S. Haldane.  Haldane was a brilliant geneticist and evolutionary biology but was also notorious for being an outspoken atheist -- something that during his lifetime (1892-1964) was seriously frowned upon.  The result was that religious types frequently showed up at his talks, whether or not the topic was religion, simply to heckle him.

At one such presentation, there was a question-and-answer period at the end, and a woman stood up and asked, "Professor Haldane, I was wondering -- what have your studies of biology told you about the nature of God?"

Without missing a beat, Haldane said, "All I can say, ma'am, is that he must have an inordinate fondness for beetles."

There's some justification for the statement.  Beetles, insects of the order Coleoptera, are the most diverse order in Kingdom Animalia, with over four hundred thousand different species known.  (This accounts for twenty-five percent of known animal species, in a single order of insects.)  The common ancestor of all modern species of beetles was the subject of an extensive genetic study in 2018 by Zhang et al., which found that the first beetles lived in the early Permian Period, on the order of three hundred million years ago.  They survived the catastrophic bottleneck at the end of the Permian and went on to diversify more than any other animal group.

One striking-looking family in Coleoptera is Buprestidae, better known as "jewel beetles" because of their metallic, iridescent colors.  Most of them are wood-borers; a good many dig into dying or dead branches, but a few (like the notorious emerald ash borer, currently ripping its way through forests in the northern United States and Canada) are significant agricultural pests.

A few of them have colors that barely look real:

An Australian jewel beetle, Temognatha alternata [Image licensed under the Creative Commons John Hill at the English-language Wikipedia]

What's curious about this particular color pattern is that beetles apparently had a gene loss some time around the last common ancestor three hundred million years ago that knocked out the ability of the entire group to see in the blue region of the spectrum.  This kind of thing happens all the time; every species studied has pseudogenes, genetic relics left behind as non-functional copies of once-working genes that suffered mutations either to the promoter or coding regions.  However, it's odd that animals would have colors they themselves can't see, given that bright coloration is very often a signal to potential mates.

That's not the only reason for bright coloration, of course; there is also aposematic coloration (also known as warning coloration), in which flashy pigmentation is a signal that an animal is toxic or otherwise dangerous.  There, of course, it's not important to be seen by other members of your own species; all that counts is that you're visible to potential predators.  But jewel beetles aren't toxic, so their bright colors don't appear to be aposematic.

The puzzle was solved in a paper in Molecular Biology and Evolution that came out last week, in which a genetic study of jewel beetles found that unlike other beetles, they can see in the blue region of the spectrum -- and in fact, have unusually good vision in the orange and ultraviolet regions, too.  What appears to have happened is that a gene coding for a UV-sensitive protein in the eye was duplicated a couple of times (another common genetic phenomenon), and those additional copies of the gene were then free to accrue mutations and take off down their own separate evolutionary paths.  One of them gained mutations that altered the peak sensitivity of the protein into the blue region of the spectrum; the other gave their hosts the ability to see light in the orange region.

The result is that jewel beetles became tetrachromats; their eyes have acuity peaks in four different regions of the spectrum.  (Other than a few people --who themselves have an unusual mutation -- humans are trichromats, with peaks in the red, green, and blue regions.) 

What this shows is that lost genes can be recreated.  The gene loss that took out beetles' blue-light sensitivity was replaced by a duplication and subsequent mutation of a pre-existing gene.  It highlights the fundamental misunderstanding inherent in the creationists' mantra that "mutations can't create new information;" if that's not exactly what this is, there's something seriously amiss with their definition of the word "information."  (Of course, I'm sure any creationists in the studio audience -- not that there are likely to be many left -- would vehemently disagree with this.  But since willfully misunderstanding scientific research is kind of their raison d'être, that should come as no surprise to anyone.)

Anyhow, the jewel beetle study is a beautiful and elegant piece of research.  It showcases the deep link between genetics and evolution, and reminds me of the quote from Ukrainian-American biologist Theodosius Dobzhansky, which seems a fitting place to end: "Nothing in biology makes sense except in light of evolution."

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Sparkling camouflage

Natural selection is such an amazing driver of diversity.  As Richard Dawkins showed so brilliantly in his tour-de-force The Blind Watchmaker, all you have to have is an imperfect replicator and a selecting agent, and you can end up with almost any result.

The only requirement is that the change has to enhance survival and/or reproduction now.  Evolution is not forward-looking, heading in the direction of whatever would be a cool idea.  (It'd be nice if it were; I've wanted wings for ages.  Big, feathery falcon wings from my shoulders.  It'd make wearing a shirt impossible, but let's face it, I hate wearing shirts anyway so that's really not much of a sacrifice.)

Anyhow, the trick sometimes is figuring out what the benefit is, because it's not always obvious.  The extravagant tail of the peacock is clearly an attractant for females, although at this point the male peacocks may have maxed out -- reached the point where the tail's advantage of attracting females is counterbalanced by the disadvantage of being so cumbersome that it makes it harder to escape predators.  When two competing selecting agents hit that balance point, the species -- with respect to that trait, at least -- stops evolving.

A good bunch of the wild colorations you find in nature have to do with sex.  Not only attracting mates in animals, but colorful flowers attracting a specific pollinator -- because pollination is (more or less) plant sex.  But not all; the stripes of the Bengal tiger are thought to break up its silhouette in the dappled sunlight of its forest home, making it less visible to prey.  The bright colors of the dart-poison frogs are warning colorations, advertising the fact that they're highly poisonous and that predators shouldn't even think about it if they know what's good for them.  A recent study concluded that one advantage of stripes in the zebra is that it confuses biting flies, including the dangerous tsetse fly (carrier of African sleeping sickness) -- horses that were draped with striped cloth (mimicking the zebra's patterns) were far less susceptible to horsefly bites.  It's probable that the stripes also confuse predators such as lions, which frequently try to target one animal in a fleeing herd and separate it from the rest, a task that's difficult if the stripes make it hard to tell where one zebra begins and the other ends.  So zebra stripes may be a twofer.

Sometimes, though, the reason for a bright coloration isn't obvious.  In the summer here in upstate New York we often see brilliant little tiger beetles, named not for stripes (most of them don't have 'em) but for their role as a voracious predator of other insects.  The ones we have here are a glistening emerald green, which I always figured camouflaged them on plant leaves -- but there are ones that are an iridescent blue, and one species is green and blue with orange spots.

Hard to call that camouflage.

[Image licensed under the Creative Commons Ryan Hodnett, Six-spotted Tiger Beetle (Cicindela sexguttata) - Mississauga, Ontario 01, CC BY-SA 4.0]

Turns out that even the non-green ones might be using their sparkling colors as camouflage, however implausible that sounds.  A study that appeared this week in Current Biology, led by Karin Kjernsmo of the University of Bristol, concluded that the iridescence itself confuses predators, as much as it seems like it would attract attention.

Kjernsmo was studying the aptly-named Asian jewel beetles, which like our North American tiger beetles come in a wide range of glittering colors.  She took the wing cases of jewel beetles, both the iridescent and the matte species, and baited them with mealworms to see if birds had a preference.  85% of the targets with matte wings (of various colors) were picked off by birds, while only 60% of the iridescent ones were.

"It may not sound like much," Kjernsmo said, "but just imagine what a difference this would make over evolutionary time."

Her next question, though, was why.  This is much harder to determine, mostly because you can't ask a bird why it picked a particular insect for lunch.  (Well, you can ask.)  So what she did was a simple but suggestive experiment using human subjects -- she stuck various-colored wing cases to leaves at eye level on a forest trail, and had thirty-six human subjects walk the trail and see how many they could find.  They found 80% of the matte ones -- and only 17% of the iridescent ones!

It's a surprising result.  It may be that the shifting, sparkling surface of an iridescent insect confounds the ability of your visual cortex to make sense of what it's seeing by rendering it more difficult to perceive the edges, and therefore the shape, of what you're looking at.  The result: you can see the colors, but you don't recognize it as a beetle.  It's a plausible guess, but it will take more research to find out if it's the correct one, and if the reason the humans couldn't see iridescent wings is the same as why birds didn't eat them.

But once again, we're left with a slight difference in selection by a predator leading to what Darwin called "endless forms most beautiful and most wonderful."  The natural world is deeply fascinating, and is even more wonderful when you not only can appreciate its beauty -- but understand where that beauty may have come from.

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The brilliant, iconoclastic physicist Richard Feynman was a larger-than-life character -- an intuitive and deep-thinking scientist, a prankster with an adolescent sense of humor, a world traveler, a wild-child with a reputation for womanizing.  His contributions to physics are too many to list, and he also made a name for himself as a suspect in the 1950s "Red Scare" despite his work the previous decade on the Manhattan Project.  In 1986 -- two years before his death at the age of 69 -- he was still shaking the world, demonstrating to the inquiry into the Challenger disaster that the whole thing could have happened because of an o-ring that shattered from cold winter temperatures.

James Gleick's Genius: The Life and Science of Richard Feynman gives a deep look at the man and the scientist, neither glossing over his faults nor denying his brilliance.  It's an excellent companion to Feynman's own autobiographical books Surely You're Joking, Mr. Feynman! and What Do You Care What Other People Think?  It's a wonderful retrospective of a fascinating person -- someone who truly lived his own words, "Nobody ever figures out what life is all about, and it doesn't matter.  Explore the world.  Nearly everything is really interesting if you go into it deeply enough."

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